1. Field of the Invention
The invention relates to a method for manufacturing a saddle-shaped coil and more particularly to a method for manufacturing a saddle-shaped coil for an electromagnetic deflection unit for deflecting the electron beam or beams of electron beam tubes which are used for displaying pictures in television receivers.
2. Background of the Invention
With the advent of picture display tubes having a large maximum deflection angle in the field of television reception, it has become more and more difficult to reproducibly manufacture electromagnetic deflection units which deflect the electron beam or beams of said tubes in the correct manner to provide a commercially acceptable television frame on the associated screen. An electromagnetic deflection unit normally comprises two pairs of deflection coil units. One pair of coil units is used for providing the vertical deflection of the electron beam(s), while the other pair is used for providing the horizontal deflection of the beam(s). Display tubes which require a beam deflection over a large angle, more particularly colour television tubes in which three electron beams are used, require the generation of magnetic fields having an exactly determined configuration both by the pair of horizontal deflection coil units and by the pair of vertical coil units, in order to correctly deflect the electron beam or beams in the tube.
The coil units for the horizontal or line deflection are generally constructed so as to fit around the neck and funnel portions of the cathode-ray-tube and have saddle-shaped windings. The individual coil units are wound automatically on a winding machine. The coil units for the vertical or field deflection may also be of the saddle type, or may be of the toroidal wound type.
Saddle coils are usually wound in a two-part mould (see U.S. Pat. No. 3,086,562). The outer circumference of the aperture in which the wire is to be guided is not situated in one plane but follows an intricate path.
Wing-shaped parts are secured to the two mould halves so as to slide the wire in the aperture. The winding wire is provided with a thermoplastic bonding layer so that, after winding, a self-supporting coil can be obtained by means of heat and pressure.
In order to achieve the wire distribution required for the desired field configuration, as well as reasonable reproducibility of the coils, the utmost care should be paid to, inter alia, the shape of the moulds, the constancy of the outside wire diameter, the thickness of the layer of thermoplastic bonding material, the smoothness of the wire, the softening temperature of the bonding layer, the wire tension during winding, the temperature of the mould during winding, and the winding speed.
Tolerances in the above-mentioned parameters, and also the winding process itself and the uncontrolled sliding of the wire from the wings of the mould during winding, have so far militated against a good reproducibility. This applies particularly in the case of coils which are short compared with their winding height and the active parts (the sides) of which are curved. A good reproducibility is said to exist if in all coils of a series of deflection units each turn with the same sequency number is located in exactly the same position.
It is furthermore known from Japanese Patent Application Laid-Open No. 57-23451 (A) to wind a coil on a coil-former, in which the wire is guided and is fixed in a number of discrete points.